Mitigating the Kinetic Hindrance of Single-Crystalline Ni-Rich Cathode via Surface Gradient Penetration of Tantalum

Single-crystalline Ni-rich cathodes are promising candidates for the next-generation high-energy Li-ion batteries. However, they still suffer from poor rate capability and low specific capacity due to the severe kinetic hindrance at the nondilute state during Li⁺ intercalation. Herein, combining experiments with density functional theory (DFT) calculations, we demonstrate that this obstacle can be tackled by regulating the oxidation state of nickel via injecting high-valence foreign Ta⁵⁺ . The as-obtained single-crystalline LiNi_0.8 Co_0.1 Mn_0.1 O₂ delivers a high specific capacity (211.2 mAh g^-1 at 0.1 C), high initial Coulombic efficiency (93.8 %), excellent rate capability (157 mAh g^-1 at 4 C), and good durability (90.4 % after 100 cycles under 0.5 C). This work provides a strategy to mitigate the Li⁺ kinetic hindrance of the appealing single-crystalline Ni-rich cathodes and will inspire peers to conduct an intensive study.

Cooperative Shielding of Bi-Electrodes via In Situ Amorphous Electrode-Electrolyte Interphases for Practical High-Energy Lithium-Metal Batteries

Solid-state Li-metal batteries offer a great opportunity for high-security and high-energy-density energy storage systems. However, redundant interfacial modification layers, intended to lead to an overall satisfactory interfacial stability, dramatically debase the actual energy density. Herein, a dual-interface amorphous cathode electrolyte interphase/solid electrolyte interphase CEI/SEI protection (DACP) strategy is proposed to conquer the main challenges of electrochemical side reactions and Li dendrites in hybrid solid-liquid batteries without sacrificing energy density via LiDFOB and LiBF₄ in situ synergistic conversion. The amorphous CEI/SEI products have an ultralow mass proportion and act as a dynamic shield to cooperatively enforce dual electrodes with a well-preserved structure. Thus, this in situ DACP layer subtly reconciles multiple interfacial compatibilities and a high energy density, endowing the hybrid solid-liquid Li-metal battery with a sustainably brilliant cycling stability even at practical conditions, including high cathode loading, high voltage (4.5 V), and high temperature (45 °C) conditions, and enables a high-energy-density (456 Wh kg^-1) pouch cell (11.2 Ah, 5 mA h cm^-2) with a lean electrolyte (0.92 g Ah^-1, containing solid and liquid phases). The compatible modification strategy points out a promising approach for the design of practical interfaces in future solid-state battery systems.

Formulating the Electrolyte Towards High-Energy and Safe Rechargeable Lithium-Metal Batteries

Rechargeable lithium-metal batteries with a cell-level specific energy of >400 Wh kg^-1 are highly desired for next-generation storage applications, yet the research has been retarded by poor electrolyte-electrode compatibility and rigorous safety concerns. We demonstrate that by simply formulating the composition of conventional electrolytes, a hybrid electrolyte was constructed to ensure high (electro)chemical and thermal stability with both the Li-metal anode and the nickel-rich layered oxide cathodes. By employing the new electrolyte, Li∥LiNi_0.6 Co_0.2 Mn_0.2 O₂ cells show favorable cycling and rate performance, and a 10 Ah Li∥LiNi_0.8 Co_0.1 Mn_0.1 O₂ pouch cell demonstrates a practical specific energy of >450 Wh kg^-1 . Our findings shed light on reasonable design principles for electrolyte and electrode/electrolyte interfaces toward practical realization of high-energy rechargeable batteries.

trans-Difluoroethylene Carbonate as an Electrolyte Additive for Microsized SiOx@C Anodes

Microsized SiO_x has been vigorously investigated as an advanced anode material for next-generation lithium-ion batteries. However, its practical application is seriously hampered by its huge volume variation during the repeated (de)lithiation process, which destroys the microparticle structure and results in rapid capacity fading. Herein, we propose the usage of trans-difluoroethylene carbonate (DFEC) as an electrolyte additive to maintain the structural integrity of microsized SiO_x with a uniform carbon layer (SiO_x@C). Compared with ethylene carbonate and fluoroethylene carbonate, DFEC has lower lowest unoccupied molecular orbital energy and higher reduction potential, which is easily reduced and promotes the in situ formation of a more stable LiF-rich solid electrolyte interphase (SEI) on the surface of anode materials. The LiF-rich SEI exhibits enhanced mechanical rigidity and ionic conductivity, thus enabling the microsized SiO_x@C anodes' excellent lithium storage stability and high average Coulombic efficiency.

Revealing the Superiority of Fast Ion Conductor in Composite Electrolyte for Dendrite-Free Lithium-Metal Batteries

Composite electrolytes composed of a nanoceramic and polymer have been widely studied because of their high ionic conductivity, good Li-ion transference number, and excellent machinability, whereas the intrinsic reason for the improvement of performance is ambiguous. Herein, we have designed a functional polymer skeleton with different types of nanofiller to reveal the superiority of fast ion conductors in composite electrolyte. Three types of ceramics with different dielectric constants and Li-ion transfer ability were selected to prepare composite electrolytes, the composition, structure, and electrochemical performances of which were systematically investigated. It was found that the addition of fast ion conductive ceramics could provide a high Li-ion transference ability and decreased diffusion barrier because the additional pathways existed in the ceramic, which are revealed by experiment and density functional theory calculations. Benefiting from the superiority of fast ion conductor, Li-metal batteries with this advanced composite electrolyte exhibit an impressive cycling stability and enable a dendrite-free Li surface after cycling. Our work enriches the understanding of the function of fast ion conductors in composite electrolyte and guides the design for other high-performance composite electrolytes in rechargeable solid batteries.

Bridging Interparticle Li+ Conduction in a Soft Ceramic Oxide Electrolyte

Li⁺-conductive ceramic oxide electrolytes, such as garnet-structured Li₇La₃Zr₂O_12, have been considered as promising candidates for realizing the next-generation solid-state Li-metal batteries with high energy density. Practically, the ceramic pellets sintered at elevated temperatures are often provided with high stiffness yet low fracture toughness, making them too brittle for the manufacture of thin-film electrolytes and strain-involved operation of solid-state batteries. The ceramic powder, though provided with ductility, does not yield satisfactorily high Li⁺ conductivity due to poor ion conduction at the boundaries of ceramic particles. Here we show, with solid-state nuclear magnetic resonance, that a uniform conjugated polymer nanocoating formed on the surface of ceramic oxide particles builds pathways for Li⁺ conduction between adjacent particles in the unsintered ceramics. A tape-casted thin-film electrolyte (thickness: <10 μm), prepared from the polymer-coated ceramic particles, exhibits sufficient ionic conductivity, a high Li⁺ transference number, and a broad electrochemical window to enable stable cycling of symmetric Li/Li cells and all-solid-state rechargeable Li-metal cells.

P3/O3 Integrated Layered Oxide as High-Power and Long-Life Cathode toward Na-Ion Batteries

Low-cost and stable sodium-layered oxides (such as P2- and O3-phases) are suggested as highly promising cathode materials for Na-ion batteries (NIBs). Biphasic hybridization, mainly involving P2/O3 and P2/P3 biphases, is typically used to boost their electrochemical performances. Herein, a P3/O3 intergrown layered oxide (Na_2/3 Ni_1/3 Mn_1/3 Ti_1/3 O₂ ) as high-rate and long-life cathode for NIBs via tuning the amounts of Ti substitution in Na_2/3 Ni_1/3 Mn_{2/3- x} Ti_x O₂ (x = 0, 1/6, 1/3, 2/3) is demonstrated. The X-ray diffraction (XRD) Rietveld refinement and aberration-corrected scanning transmission electron microscopy show the co-existence of P3 and O3 phases, and density functional theory calculation corroborates the appearance of the anomalous O3 phase at the Ti substitution amount of 1/3. The P3/O3 biphasic cathode delivers an unexpected rate capability (≈88.7% of the initial capacity at a high rate of 5 C) and cycling stability (≈68.7% capacity retention after 2000 cycles at 1 C), superior to those of the sing phases P3-Na_2/3 Ni_1/3 Mn_2/3 O₂ , P3-Na_2/3 Ni_1/3 Mn_1/2 Ti_1/6 O₂ , and O3-Na_2/3 Ni_1/3 Ti_2/3 O₂ . The highly reversible structural evolution of the P3/O3 integrated cathode observed by ex situ XRD, ex situ X-ray absorption spectra, and the rapid Na⁺ diffusion kinetics, underpin the enhancement. These results show the important role of P3/O3 biphasic hybridization in designing and engineering layered oxide cathodes for NIBs.

Insights on Electrochemical Behaviors of Sodium Peroxide as a Sacrificial Cathode Additive for Boosting Energy Density of Na-Ion Battery

The development of Na-ion full cells (NIFCs) suffers from the issue that the solid electrolyte interphase formation on the carbon anode consumes the limited sodium from cathode and thus incurs the decreased energy density and poor cyclic stability. To address these issues, we herein report that Na₂O₂ could be used as a sacrificial Na source through spraying its slurry on the surface of cathode, and investigate its stability as well as electrochemical behavior toward NIFCs. The results show that Na₂O₂ has good chemical and storage stability under a dry atmosphere and has no negative effect on the electrochemical performance of the cathode. Compared with the pristine cathode, the Na₂O₂-decorated cathode exhibits higher discharge capacity, superior capacity retention, and rate capability in a full cell with a carbon anode. Our cathode Na compensation strategy provides an effective avenue to make up for the irreversible Na⁺ loss cause by the formation of solid electrolyte interphase on the anode, thereby promoting the electrochemical performance and energy density of NIFCs toward the large-scale application.

Micromechanism in All-Solid-State Alloy-Metal Batteries: Regulating Homogeneous Lithium Precipitation and Flexible Solid Electrolyte Interphase Evolution

Sulfide-based solid-state electrolytes (SSEs) matched with alloy anodes are considered as promising candidates for application in all-solid-state batteries (ASSBs) to overcome the bottlenecks of the lithium (Li) anode. However, an understanding of the dynamic electrochemical processes on alloy anode in SSE is still elusive. Herein, in situ atomic force microscopy gives insights into the block-formation and stack-accumulation behaviors of Li precipitation on an Li electrode, uncovering the morphological evolution of nanoscale Li deposition/dissolution in ASSBs. Furthermore, two-dimensional Li-indium (In) alloy lamellae and the homogeneous solid electrolyte interphase (SEI) shell on the In electrode reveal the precipitation mechanism microscopically regulated by the alloy anode. The flexible and wrinkle-structure SEI shell further enables the electrode protection and inner Li accommodation upon cycles, elucidating the functional influences of SEI shell on the cycling behaviors. Such on-site tracking of the morphological evolution and dynamic mechanism provide an in-depth understanding and thus benefit the optimizations of alloy-based ASSBs.

Dynamic Evolution of a Cathode Interphase Layer at the Surface of LiNi0.5Co0.2Mn0.3O2 in Quasi-Solid-State Lithium Batteries

Intensive understanding of the surface mechanism of cathode materials, such as structural evolution and chemical and mechanical stability upon charging/discharging, is crucial to design advanced solid-state lithium batteries (SSLBs) of tomorrow. Here, via in situ atomic force microscopy monitoring, we explore the dynamic evolution process at the surface of LiNi_0.5Co_0.2Mn_0.3O₂ cathode particles inside a working SSLB. The dynamic formation process of the cathode interphase layer, with an inorganic-organic hybrid structure, was real-time imaged, as well as the evolution of its mechanical property by in situ scanning of the Derjaguin-Muller-Toporov modulus. Moreover, different components of the cathode interphase layer, such as LiF, Li₂CO₃, and specific organic species, were identified in detailat different stages of cycling, which can be directly correlated with the impedance buildup of the battery. In addition, the transition metal migration and the formation of new phases can further exacerbate the degradation of the SSLB. A relatively stable cathode interphase is key to improving the performance of SSLBs. Our findings provide deep insights into the dynamic evolution of surface morphology, chemical components and mechanical properties of the cathode interphase layer, which are pivotal for the performance optimization of SSLBs.

Interfacial Evolution of Lithium Dendrites and Their Solid Electrolyte Interphase Shells of Quasi-Solid-State Lithium-Metal Batteries

Unstable electrode/solid-state electrolyte interfaces and internal lithium dendrite penetration hamper the applications of solid-state lithium-metal batteries (SSLMBs), and the underlying mechanisms are not well understood. Herein, in situ optical microscopy provides insights into the lithium plating/stripping processes in a gel polymer electrolyte and reveals its dynamic evolution. Spherical lithium deposits evolve into moss-like and branch-shaped lithium dendrites with increasing current densities. Remarkably, the on-site-formed solid electrolyte interphase (SEI) shell on the lithium dendrite is distinctly captured after lithium stripping. Inducing an on-site-formed SEI shell with an enhanced modulus to wrap the lithium precipitation densely and uniformly can regulate dendrite-free behaviors. An in-depth understanding of lithium dendrite evolution and its functional SEI shell will aid in the optimization of SSLMBs.

High-Efficiency Cathode Sodium Compensation for Sodium-Ion Batteries

Sodium-ion batteries have gained much attention for their potential application in large-scale stationary energy storage due to the low cost and abundant sodium sources in the earth. However, the electrochemical performance of sodium-ion full cells (SIFCs) suffers severely from the irreversible consumption of sodium ions of cathode during the solid electrolyte interphase (SEI) formation of hard carbon anode. Here, a high-efficiency cathode sodiation compensation reagent, sodium oxalate (Na₂ C₂ O₄ ), which possesses both a high theoretical capacity of 400 mA h g^-1 and a capacity utilization as high as 99%, is proposed. The implementation of Na₂ C₂ O₄ as sacrificial sodium species is successfully realized by decreasing its oxidation potential from 4.41 to 3.97 V through tuning conductive additives with different physicochemical features, and the corresponding mechanism of oxidation potential manipulation is analyzed. Electrochemical results show that in the full cell based on a hard carbon anode and a P2-Na_2/3 Ni_1/3 Mn_1/3 Ti_1/3 O₂ cathode with Na₂ C₂ O₄ as a sodium reservoir to compensate for sodium loss during SEI formation, the capacity retention is increased from 63% to 85% after 200 cycles and the energy density is improved from 129.2 to 172.6 W h kg^-1 . This work can provide a new avenue for accelerating the development of SIFCs.

Enabling SiOx/C Anode with High Initial Coulombic Efficiency through a Chemical Pre-Lithiation Strategy for High-Energy-Density Lithium-Ion Batteries

Carbon-coated SiO_x microparticles (SiO_x/C) demonstrate attractive potential for anode use in high-energy-density lithium-ion batteries due to high capacity and proper cycling stability. However, the excessive irreversible consumption of Li ions during the initial cycling remains a serious challenge arising from the limited lithium in full cells. Here, we endow SiO_x/C anode with high initial Coulombic efficiency using the chemical pre-lithiation strategy. The lithium silicate is uniformly pregenerated in SiO_x/C microparticles, which could effectively counteract the irreversible consumption of Li ions and avoid the complicated pre-lithiation process. Moreover, this strategy guarantees the structural integrity and processability of anode materials because of the homogeneous Li-organic complex solution pre-lithiation and high-temperature calcination process. The obtained SiO_x/C microparticles can be applied as anode materials by directly mixing with commercial graphite, which demonstrates proper specific capacity, high initial Coulombic efficiency, and excellent cycling performance. Furthermore, the pouch cells using LiNi_0.8Co_0.1Mn_0.1O₂ cathodes and the as-prepared anodes exhibit high energy density (301 Wh kg^-1) and satisfactory cycling stability (93.3% capacity retention after 100 cycles).

A Rational Reconfiguration of Electrolyte for High-Energy and Long-Life Lithium-Chalcogen Batteries

Lithium-chalcogen batteries are an appealing choice for high-energy-storage technology. However, the traditional battery that employs liquid electrolytes suffers irreversible loss and shuttle of the soluble intermediates. New batteries that adopt Li⁺ -conductive polymer electrolytes to mitigate the shuttle problem are hindered by incomplete discharge of sulfur/selenium. To address the trade-off between energy and cycle life, a new electrolyte is proposed that reconciles the merits of liquid and polymer electrolytes while resolving each of their inferiorities. An in situ interfacial polymerization strategy is developed to create a liquid/polymer hybrid electrolyte between a LiPF₆ -coated separator and the cathode. A polymer-gel electrolyte in situ formed on the separator shows high Li⁺ transfer number to serve as a chemical barrier against the shuttle effect. Between the gel electrolyte and the cathode surface is a thin gradient solidification layer that enables transformation from gel to liquid so that the liquid electrolyte is maintained inside the cathode for rapid Li⁺ transport and high utilization of active materials. By addressing the dilemma between the shuttle chemistry and incomplete discharge of S/Se, the new electrolyte configuration demonstrates its feasibility to trigger higher capacity retention of the cathodes. As a result, Li-S and Li-Se cells with high energy and long cycle lives are realized, showing promise for practical use.

An Outlook on Low-Volume-Change Lithium Metal Anodes for Long-Life Batteries

Rechargeable Li metal batteries are one of the most attractive energy storage systems due to their high energy density. However, the hostless nature of Li, the excessive dendritic growth, and the accumulation of nonactive Li induce severe volume variation of Li anodes. The volume variation can give rise to a fracture of solid electrolyte interphase, continuous consumption of Li and electrolytes, low Coulombic efficiency, fast performance degradation, and finally short cycle life. This Outlook provides a comprehensive understanding of the origin and consequences of Li volume variation. Recent strategies to address this challenge are reviewed from liquid to gel to solid-state electrolyte systems. In the end, guidelines for structural design and fabrication suggestions for future long-life Li composite anodes are presented.

Building an Air Stable and Lithium Deposition Regulable Garnet Interface from Moderate-Temperature Conversion Chemistry

Garnet-type electrolytes suffer from unstable chemistry against air exposure, which generates contaminants on electrolyte surface and accounts for poor interfacial contact with the Li metal. Thermal treatment of the garnet at >700 °C could remove the surface contaminants, yet it regenerates the contaminants in the air, and aggravates the Li dendrite issue as more electron-conducting defective sites are exposed. In a departure from the removal approach, here we report a new surface chemistry that converts the contaminants into a fluorinated interface at moderate temperature <180 °C. The modified interface shows a high electron tunneling barrier and a low energy barrier for Li⁺ surface diffusion, so that it enables dendrite-proof Li plating/stripping at a high critical current density of 1.4 mA cm^-2 . Moreover, the modified interface exhibits high chemical and electrochemical stability against air exposure, which prevents regeneration of contaminants and keeps high critical current density of 1.1 mA cm^-2 . The new chemistry presents a practical solution for realization of high-energy solid-state Li metal batteries.

Direct regeneration of spent LiFePO4via a graphite prelithiation strategy

A new, low-cost and green regeneration method was developed to revive spent LiFePO₄-based batteries.

Large-Scale Synthesis of the Stable Co-Free Layered Oxide Cathode by the Synergetic Contribution of Multielement Chemical Substitution for Practical Sodium-Ion Battery

The O3-type layered oxide cathodes for sodium-ion batteries (SIBs) are considered as one of the most promising systems to fully meet the requirement for future practical application. However, fatal issues in several respects such as poor air stability, irreversible complex multiphase evolution, inferior cycling lifespan, and poor industrial feasibility are restricting their commercialization development. Here, a stable Co-free O3-type NaNi_0.4Cu_0.05Mg_0.05Mn_0.4Ti_0.1O₂ cathode material with large-scale production could solve these problems for practical SIBs. Owing to the synergetic contribution of the multielement chemical substitution strategy, this novel cathode not only shows excellent air stability and thermal stability as well as a simple phase-transition process but also delivers outstanding battery performance in half-cell and full-cell systems. Meanwhile, various advanced characterization techniques are utilized to accurately decipher the crystalline formation process, atomic arrangement, structural evolution, and inherent effect mechanisms. Surprisingly, apart from restraining the unfavorable multiphase transformation and enhancing air stability, the accurate multielement chemical substitution engineering also shows a pinning effect to alleviate the lattice strains for the high structural reversibility and enlarges the interlayer spacing reasonably to enhance Na⁺ diffusion, resulting in excellent comprehensive performance. Overall, this study explores the fundamental scientific understandings of multielement chemical substitution strategy and opens up a new field for increasing the practicality to commercialization.